The present invention relates to wireless telephony equipment, and more particularly to an improved arrangement for providing antenna diversity using remote transceivers in a wireless telephone system that incorporates an existing broadband distribution network, such as a cable television network cable, to carry communication signals between wireless telephones and centrally located telephony equipment.
The prior art teaches the use of an existing broadband network to carry telephony signals between an existing telephone network and a large number of remote transceivers positioned to provide signal coverage in defined cells or sectors. The remote transceivers, sometimes called Remote Antenna Drivers (RADs), are used to establish wireless telephony communication links with wireless telephones operating with a defined area covered by each RAD. The broadband networks include fiber-optic cable, coaxial cable, radio links and combinations of these.
Between the telephone network and the broadband network is centrally located equipment which is part of the wireless telephony equipment, and which processes and carries the telephony signals between the telephone network and the broadband distribution network.
A large number of distributed remote transceivers, also called Remote Antenna Drivers (RADs) are connected to the broadband distribution network. The RADs communicate via the broadband distribution network with Remote Antenna Signal Processors (RASPs), which are a centrally located part of the wireless telephony equipment. The RADs and RASPs use radio frequency carrier signals to carry telephony signals over the broadband distribution network. The RASPs in turn communicate with the telephone network via a Base Telephone Station (BTS). The RADs, RASPs and BTS cooperate to carry telephony signals between wireless telephones and the telephone network. The RADs transmit radio frequency signals to, and receive radio frequency signals from wireless telephones in a manner well known in the art.
In the prior art each RAD has two antennas for receiving telephony signals from wireless telephones, and the signals from all receive antennas are concurrently transmitted over the broadband distribution network to the centrally located RASP and BTS for signal processing before the telephony signals are sent to the telephone network. Typically, one of the two receive antennas is called the primary receive antenna and the other receive antenna is called the diversity receive antenna. These two antennas are physically spaced and cooperate to minimize signal fading, and thereby provide continuous signal reception from wireless telephones.
The use of two receive antennas in each RAD requires duplicate receive circuitry therein, which increases the cost of each RAD. In addition, each RASP must process two received telephony signals from each RASP for each wireless telephone. This also requires duplicate circuitry which increases the cost of each RASP. Thus, there is a need in the art for simpler, less expensive RADs and RASPs, while not sacrificing signal reception from wireless telephones.
The above described need in the wireless telephony art is satisfied by the present invention. The Remote Antenna Drivers (RADs) and the Remote Antenna Signal Processors (RASPs) are made simpler, deleting duplicate circuitry, while not sacrificing good received signal reception from wireless telephones.
In existing wireless telephony systems, of the type described above, there are two antennas on each RAD for receiving signals from wireless telephones. These two antennas are called the primary and diversity antennas and are spaced from each other. Typically, even when a wireless telephone is xe2x80x9cwithin rangexe2x80x9d of a RAD its received signal strength from one antenna may fade while the received signal from the other antenna remains strong. The RAD returns both received signals to its associated RASP and BTS where the two signals are combined with the overall result being no signal fading.
In implementing the present invention, in each of the RADs one of the two receive antennas and all of its associated circuitry is eliminated. Accordingly, with each RASP not having to process two signals from each RAD for each wireless telephone call, the circuitry in each RASP is greatly simplified with a corresponding cost saving.
To compensate for the signal fading problem without two receive antennas on each RAD, RADs are placed closer together so they have coverage areas that overlap more than provided in the prior art. Thus, adjacent RADS receive signals from a wireless telephone and concurrently transmit the signals to the RASP. By having more closely spaced RADs there are fewer dead spots where signal coverage is not provided by any RAD. This is a problem well known in the art. The improved area coverage and equipment cost savings are accomplished without increasing the service load on the wireless telephone system. In addition, the BTS need not be changed, and can function with prior art RADs and RASPs or RADs and RASPs implementing the present invention. Furthermore, a greater area is covered with the same reverse bandwidth in the broadband network.
As is known in the art, RADs are spaced along the broadband distribution network cable, and their individual areas of coverage overlap somewhat to provide continuous signal coverage when handing off calls, but not for extended coverage overlap. In implementing the present invention RADs are placed closer together as mentioned above. With RADs being spaced closer together, signals from a wireless telephone are received by more than one RAD at a time. Adjacent RADs receiving signals from a wireless telephone each forward the signals via the broadband network to the RASP associated with the RADs. Diversity is achieved by alternating primary and diversity assignments across adjacent RADs. This operation provides reverse link site diversity and the same reliable, continuous signal coverage as when there is a primary and diversity receive antenna on each RAD.
Also, as is known in the art, one reverse frequency channel is used for the primary, and another for the diversity antenna, for each RAD. In implementing the present invention, each RAD has only one receive antenna, and adjacent RADs are assigned either primary or diversity roles. As a result of the invention, more RADs are served by the same reverse bandwidth (i.e. primary and diversity reverse channels) in the broadband network.
In accordance with the teaching of the present invention, the one receive antenna on a first RAD acts as a primary antenna, while the one receive antenna on a second, adjacent RAD acts as the diversity antenna to the first RAD, and so on in an alternating fashion between RADS along the Broadband Distribution Network.
Due to the overlapping signal coverage of the more closely spaced RADs, and signals from a wireless telephone being forwarded by more than one RAD to the RASP and BTS, the telephony signals are combined, just as in the prior art. Thus, the advantage of the primary and diversity receive antenna RADs is maintained.